Fix uninitialized variable added in b33b9a6fe

After discussing with BlueMatt, this appears to be harmless in its
current state since it's always set before it's used. Initialize it
anyway for readability and future safety.

Rebased-from: 106f133de6bdb577c4135847fd703d08f525ba46
Add some additional logging to give extra network insight.
leveldb: Use native Darwin memory barriers